Methods for operating a mobile station and a base station in a radio communication system, mobile station and base station thereof

ABSTRACT

The embodiments of the invention relate to a method for operating a mobile station (MS) in a radio communication system (RAN). The method contains receiving first radio resource information for a transmission of first reference signals via a first radiation beam (BM1-BS1) being directed towards a first direction by at least one neighboring base station (BS1) of a serving base station (BS2) of the mobile station (MS) and at least second radio resource information for a transmission of at least second reference signals via at least one second radiation beam (BM2-BS1, . . . BM5-BS1) being directed towards at least one second direction by the at least one neighboring base station (BS1). The method further contains receiving the first reference signals based on the first radio resource information, receiving the at least second reference signals based on the at least second radio resource information, determining first quality information of the first radiation beam (BM1-BS1) based on the received first reference signals and at least second quality information of the at least second radiation beam (BM2-BS1, . . . BM5-BS1) based on the received at least second reference signals, and transmitting at least one of the first quality information and the at least second quality information to the serving base station (BS2). The embodiments further relate to a method for operating a base station (BS2) in a radio communication system (RAN), to a mobile station (MS) for operation in a radio communication system (RAN) and to a base station (BS2) for operation in a radio communication system (RAN).

FIELD OF THE INVENTION

The present invention relates to a handover or cell re-association in aradio communication system and, more particularly but not exclusively,to a handover or cell re-association of a mobile station to a basestation using at least two vertical radiation beams.

BACKGROUND

This section introduces aspects that may be helpful in facilitating abetter understanding of the invention. Accordingly, the statements ofthis section are to be read in this light and are not to be understoodas admission about what is in the prior art.

Future radio communication networks may have a mixture of conventionalfirst base stations being adapted to transmit radiation beams to severalso-called horizontal directions but to only one so-called verticaldirection and further more sophisticated second base stations beingadapted to transmit so-called horizontal radiation beams to severalhorizontal directions and further being adapted to transmit so-calledvertical radiation beams to several vertical directions. Horizontaldirection means in the following a direction, which may be defined by anazimuth angle between a surface normal of a radiating surface of anantenna system and a beam direction of a horizontal beam. Verticaldirection means in the following a direction, which is defined by anelevation angle between the surface normal of the radiating surface ofthe antenna system and a beam direction of a vertical beam.

When such a second base station transmits time multiplexed common pilotsa mobile station which arrives in a coverage area of the second basestation would observe only an aggregated vertical radiation beam bymeasuring the different pilots over a certain period of time and wouldbe not aware of the several vertical radiation beams. Thus, the mobilestation or a base station currently serving the mobile station mayselect a target radio cell of a further second base station for ahandover, although one of the several vertical radiation beams of thesecond base station is directly pointing to the mobile station.Furthermore, the serving base station might not know an impact ofinterference caused by the several vertical radiation beams at variouslocations in its own serving radio cell.

In current 3GPP standards (3GPP=3rd Generation Partnership Project),only two radiation beams with a first and a second measurement area canbe supported based on time domain RS and CQI measurements (RS=ReferenceSymbols, CQI=Channel Quality Identifier) which have been originallyintroduced for eICIC (eICIC=enhanced Inter Cell InterferenceCoordination). Instead of using the two measurement areas for aso-called ABS (ABS=Almost Blank Subframe) and a so-called non-ABS, thetwo measurement areas may be used for upper beam and lower beam.However, in current 3GPP standards such two measurement areas are onlysupported for CQI measurements inside a current serving cell and not fora handover to a target cell. Furthermore, not more than two radiationbeams can be supported by such a technical consideration.

The best existing solution in case of having more than two verticalradiation beams at a target base station would be to measure averagesignal strength over all the vertical radiation beams which may lead toa non-optimal handover decision and a non-optimal radio cell selectionand cell association. Another solution would be to define every of thevertical radiation beams as a separate radio cell. However, this wouldlead to many handovers and to a non optimal throughput performance,because a time consuming handover would be required in order to use theoptimal beam and a fast switching between the radiation beams would benot possible.

US 2009/0264118 A1 discloses a method of generating neighbor lists in aradio communication network comprising user terminals and base stationsdefining sectored or omnidirectional radio cells. The method comprisesthe steps of receiving radio channel measurements from at least some ofthe user terminals, creating a first table which comprises for at leastsome of the user terminals the corresponding radio channel measurementin relation to different radio cells, processing the first table togenerate a cell coupling matrix comprising coupling figures betweendifferent pairs of cells and obtaining for a certain cell a neighborlist which contains neighbor that have a coupling figure greater than agiven threshold.

SUMMARY

Thus, an object of the embodiments of the invention is to provide animproved handover or cell re-association in a radio communication systemand especially in those radio communication systems which consist of amixture of radio cells being served by several vertical radiation beamsand of further radio cells being served by only one vertical radiationbeam. A further object of the embodiments of the invention is to reducean impact of the interference of the various vertical radiation beams ofa first radio cell within a coverage area of a neighbouring second radiocell for improving a scheduling of mobile stations by a base stationwhich serves the second radio cell.

The object is achieved by a method for operating a mobile station in aradio communication system. The method contains receiving from a servingbase station of the mobile station first radio resource information fora transmission of first reference signals via a first radiation beambeing by an antenna array directed towards a first direction and beingaligned with respect to a first elevation angle by at least oneneighboring base station of the serving base station and at least secondradio resource information for a transmission of at least secondreference signals by the antenna array via at least one second radiationbeam being directed towards at least one second direction by the atleast one neighboring base station and being aligned with respect to asecond elevation angle different to the first elevation angle. Themethod further contains receiving the first reference signals based onthe first radio resource information and receiving the at least secondreference signals based on the at least second radio resourceinformation. The method even further contains determining first qualityinformation of the first radiation beam based on the received firstreference signals and at least second quality information of the atleast second radiation beam based on the received at least secondreference signals and transmitting at least one of the first qualityinformation and the at least second quality information to the servingbase station. Serving base station means here a prior serving basestation before a handover of the mobile station may be executed to theat least one neighboring base station, which is after the handover asuccessive serving base station for the mobile station.

The object is further achieved by a method for operating a base stationin a radio communication system. The method contains transmitting to amobile station being served by the base station first radio resourceinformation for a transmission of first reference signals by an antennaarray via a first radiation beam being directed by at least oneneighboring base station of the base station towards a first directionand being aligned with respect to a first elevation angle and at leastsecond radio resource information for a transmission of at least secondreference signals by the antenna array via at least one second radiationbeam being directed by the at least one neighboring base station towardsat least one second direction and being aligned with respect to a secondelevation angle different to the first elevation angle. The methodfurther contains receiving from the mobile station at least one of afirst quality information of the first radiation beam and of at leastsecond quality information of the at least one second radiation beam.The method even further contains determining based on the at least oneof the first quality information and the at least second qualityinformation, whether a further scheduling of the mobile station by thebase station or a handover of the mobile station to the at least oneneighboring base station is more suitable.

The object is even further achieved by a mobile station for operation ina radio communication system. The mobile station contains means forreceiving from a serving base station of the mobile station first radioresource information for a transmission of first reference signals by anantenna array via a first radiation beam being directed by at least oneneighboring base station of the serving base station towards a firstdirection and being aligned with respect to a first elevation angle andat least second radio resource information for a transmission of atleast second reference signals by the antenna array via at least onesecond radiation beam directed by the at least one neighboring basestation towards at least one second direction and being aligned withrespect to a second elevation angle different to the first elevationangle and for receiving the first reference signals based on the firstradio resource information and for receiving the at least secondreference signals based on the at least second radio resourceinformation. The mobile station even further contains means fordetermining first quality information of the first radiation beam basedon the received first reference signals and at least second qualityinformation of the at least second radiation beam based on the receivedat least second reference signals. The mobile station even furthercontains means for transmitting at least one of the first qualityinformation and of the at least second quality information to theserving base station.

In embodiments, the means for receiving may correspond to any receiver,transceiver, receiver unit, transceiver module etc. Hence, inembodiments the means for receiving may contain an input for receivedsignals such as radio frequency signals which are modulated with thefirst radio resource information, with the at least second radioresource information, with the first reference signals and/or with theat least second reference signals, a pre-amplifier for the receivedsignals, an algorithm, which extracts the first radio resourceinformation, the at least second radio resource information, the firstreference signals and/or the at least second reference signals from thereceived signals, and an output for the first radio resourceinformation, the at least second radio resource information, the firstreference signals and/or the at least second reference signals. In someembodiments the means for receiving can be implemented partly in termsof a computer program and a hardware component on which the computerprogram is executed, such as a DSP (DSP=Digital Signal Processor), anASIC (ASIC=Application-Specific Integrated Circuit), an FPGA(FPGA=Field-Programmable Gate Array) or any other processing unit.

In embodiments, the means for determining may correspond to anydetermination unit, determination module, etc. Hence, in embodiments themeans for determining may contain an input for the received firstreference signals and the received at least second reference signals, analgorithm, which determines the first quality information and the atleast second quality information using the received first referencesignals and the received second reference signals, and an output for thefirst quality information and the at least second quality information.In some embodiments the means for determining can be implemented interms of a computer program and a hardware component on which thecomputer program is executed, such as a DSP, an ASIC, an FPGA or anyother processing unit.

In embodiments, the means for transmitting the at least one of the firstquality information and of the at least second quality information maycorrespond to any transmitter unit, transmitter module, transceiverunit, transceiver module etc. which contains a digital processing partand an analogue processing part with a power amplifier. Hence, inembodiments the means for transmitting may contain an input for the atleast one of the first quality information and of the at least secondquality information, an algorithm which modulates a signal with the atleast one of the first quality information and of the at least secondquality information and generates a radio frequency signal, a poweramplifier which amplifies the radio frequency signal, and an output forthe radio frequency signal. In some embodiments the means fortransmitting can be partly implemented in terms of a computer programand a hardware component on which the computer program is executed, suchas a DSP, an ASIC, an FPGA or any other processing unit.

The object is even further achieved by a base station for operation in aradio communication system. The base station contains means fortransmitting to a mobile station being served by the base station firstradio resource information for a transmission of first reference signalsby an antenna array via a first radiation beam being directed by atleast one neighboring base station of the base station towards a firstdirection and being aligned with respect to a first elevation angle andat least second radio resource information for a transmission of atleast second reference signals by the antenna array via at least onesecond radiation beam being directed by the at least one neighboringbase station towards at least one second direction and being alignedwith respect to a second elevation angle different to the firstelevation angle. The base station further contains means for receivingfrom the mobile station at least one of a first quality information ofthe first radiation beam and of at least second quality information ofthe at least one second radiation beam. The base station even furthercontains means for determining based on the at least one of the firstquality information and the at least second quality information, whethera further scheduling of the mobile station by the base station or ahandover of the mobile station to the at least one neighboring basestation is more suitable.

In embodiments, the means for transmitting the first radio resourceinformation and the at least second radio resource information maycorrespond to any transmitter unit, transmitter module, transceiverunit, transceiver module etc. which contains a digital processing partand an analogue processing part with a power amplifier. Hence, inembodiments the means for transmitting may contain an input for thefirst radio resource information and the at least second radio resourceinformation, an algorithm which modulates at least one signal with thefirst radio resource information and/or the at least second radioresource information and generates at least one radio frequency signal,a power amplifier which amplifies the at least one radio frequencysignal, and an output for the at least one radio frequency signal. Insome embodiments the means for transmitting can be partly implemented interms of a computer program and a hardware component on which thecomputer program is executed, such as a DSP, an ASIC, an FPGA or anyother processing unit.

In embodiments, the means for receiving may correspond to any receiver,transceiver, receiver unit, transceiver module etc. Hence, inembodiments the means for receiving may contain an input for receivedsignals such as radio frequency signals which are modulated with the atleast one of the first quality information and the at least secondquality information, a pre-amplifier for the received signals, analgorithm, which extracts the at least one of the first qualityinformation and the at least second quality information from thereceived signals, and an output for the at least one of the firstquality information and the at least second quality information. In someembodiments the means for receiving can be implemented partly in termsof a computer program and a hardware component on which the computerprogram is executed, such as a DSP, an ASIC, an FPGA or any otherprocessing unit.

In embodiments, the means for determining may correspond to anydetermination unit, determination module, etc. Hence, in embodiments themeans for determining may contain an input for the at least one of thefirst quality information and the at least second quality information,an algorithm, which verifies using the at least one of the first qualityinformation and the at least second quality information whether afurther scheduling of the mobile station by the base station or ahandover of the mobile station towards the at least one neighbouringbase station is more suitable, and an output for the first qualityinformation and the at least second quality information. In someembodiments the means for determining can be implemented in terms of acomputer program and a hardware component on which the computer programis executed, such as a DSP, an ASIC, an FPGA or any other processingunit.

The embodiments provide as a first advantage an improved handover orcell re-association in radio communication systems and especially inthose radio communication systems, which consist of a mixture of radiocells being served by several vertical radiation beams and of furtherradio cells being served by only one vertical radiation beam. Theembodiments even further provide as a second advantage knowledge at theserving base station of the mobile station about the interference, whichis caused by the various vertical radiation beams of the neighbouringbase station. Thereby, the serving base station may be able to optimizea scheduling of the mobile station in its own serving radio cell. Anoptimized scheduling yields a higher throughput in the serving radiocell. The embodiments even further provide as a third advantage a betterdecision for a re-association of the mobile station to the neighbouringbase station, which transmits the several vertical radiation beams.Thereby, an overall data throughput of the radio communication systemmay be achieved. Especially mobile stations, which are located at a cellborder may be served with a higher data throughput. According to afurther advantage, the embodiments are independent of a special RSdesign for vertical radiation beams as long as a mobile station is ableto make separate measurements for the vertical radiation beams of aradio cell of the at least one neighboring base station.

In a further embodiment the method further contains the steps ofreceiving at the at least one neighboring base station from the mobilestation further quality information for the first radiation beam and forthe at least second radiation beam and determining at the at least oneneighboring base station an alternative radiation beam for schedulingthe mobile station based on the further quality information, when thealternative radiation beam provides a higher quality than the initialserving radiation beam.

Preferably, the higher quality corresponds to a larger data throughputfor scheduling the mobile station via the alternative radiation beamthan scheduling the mobile station via the initial serving radiationbeam.

In an even further embodiment, the method further contains the steps ofreceiving at the at least one neighboring base station a request fromthe serving base station for first radio resource information for atransmission of the first reference signals via the first radiation beamand for at least one second radio resource information for atransmission of the at least second reference signals via the at leastone second radiation beam, and transmitting from the at least oneneighboring base station to the serving base station a reply, whichcontains the first radio resource information and the at least onesecond radio resource information.

According to further embodiments the transmitting of the first referencesignals and the at least second reference signals contains transmittingthe first reference signals and the at least second reference signals byat least two time resources, by at least two frequency resources, by atleast two code resources or by at least two sets of time resources andfrequency resources.

According to a further embodiment, the method further contains the stepsof transmitting from the serving base station to the at least oneneighboring base station a request for information about a usage of thefirst radiation beam and of the at least one second radiation beam bythe at least one at least one neighboring base station, and receiving atthe serving base station from the at least one neighboring base stationa reply with the information.

Preferably the usage information contains information about a schedulingof further mobile stations at the at least one neighboring base stationvia the first radiation beam and/or via the at least one secondradiation beam.

The further embodiment provides as a further advantage knowledge at theserving base station of the mobile station about the interference, whichis caused by the various vertical radiation beams of the neighbouringbase station. Thereby, the serving base station may be able to optimizea scheduling of the mobile station in its own serving radio cell. Anoptimized scheduling yields a higher throughput in the serving radiocell.

According to an even further embodiment the method further contains thesteps of scheduling at the serving base station the mobile station fordownlink data based on the quality information in a time slot, when ausage of one of the first radiation beam and of the at least one secondradiation beam by the at least one neighboring base station fulfills apredefined criterion and when a handover decision for the mobile stationis pending.

Preferably the predefined criterion is an availability of information atthe serving base station that one of the first radiation beam and of theat least one second radiation beam with a largest interference at alocation of the mobile station is currently not used.

According to a further embodiment, the method further contains the stepsof preventing at the serving base station a scheduling of the mobilestation for uplink data in at least one time slot, when the usage of oneof the first radiation beam and of the at least one second radiationbeam fulfills the predefined criterion and when during the at least onetime slot uplink data are transmitted from at least one further mobilestation to the at least one neighboring base station.

Further advantageous features of the embodiments of the invention aredefined in the dependent claims and are described in the followingdetailed description.

BRIEF DESCRIPTION OF THE FIGURES

The embodiments of the invention will become apparent in the followingdetailed description and will be illustrated by accompanying figuresgiven by way of non-limiting illustrations.

FIG. 1 shows schematically a radio access network which contains a firstbase station adapted to transmit several vertical radiation beams, asecond base station adapted to transmit a single vertical radiation beamand a mobile station, which is located between the first base stationand the second base station.

FIG. 2 shows schematically a flow diagram of a method for a mobilestation for radiation beam selection in a radio communication system.

FIG. 3 shows schematically a flow diagram of a method for a second basestation for radiation beam selection in a radio communication system.

FIG. 4 shows schematically a flow diagram of a method for a first basestation for radiation beam selection in a radio communication system.

FIG. 5 shows schematically a block diagram of a mobile station beingadapted for radiation beam selection in a radio communication system.

FIG. 6 shows schematically a block diagram of a second base stationbeing adapted for radiation beam selection in a radio communicationsystem.

FIG. 7 shows schematically a block diagram of a first base station beingadapted for radiation beam selection in a radio communication system.

DESCRIPTION OF THE EMBODIMENTS

The description and drawings merely illustrate the principles of theinvention. It will thus be appreciated that those skilled in the artwill be able to devise various arrangements that embody the principlesof the invention. Furthermore, all examples recited herein areprincipally intended expressly to be only for pedagogical purposes toaid the reader in understanding the principles of the invention and theconcepts contributed by the inventors to furthering the art, and are tobe construed as being without limitation to such specifically recitedexamples and conditions. A splitting of processing functions acrossprocessing units shown in the Figures is not critical, and as can beunderstood by those skilled in the art that the number of processingunits, the number of processing functions and an allocation of theprocessing functions to the processing units may vary without departingfrom the scope of the embodiments of the invention as defined in theappended claims. The number of the steps for performing the method(s) isnot critical, and as can be understood by those skilled in the art thatthe number of the steps and the sequence of the steps may vary withoutdeparting from the scope of the embodiments of the invention as definedin the appended claims.

FIG. 1 shows schematically a radio access network RAN which contains afirst base station BS1 which is adapted to transmit several verticalradiation beams BM1-BS1, . . . , BM5-BS1 by applying for example aso-called vertical pre-coding.

Alternatively, the first base station BS1 may be adapted to transmit theseveral vertical radiation beams BM1-BS1, . . . , BM5-BS1 and inaddition several horizontal radiation beams according to a so-calledMIMO transmission scheme (MIMO=Multiple Input Multiple Output) (theseveral horizontal radiation beams are not shown in FIG. 1 forsimplification.

The radio access network RAN further contains a second base station BS2which is adapted to transmit a single vertical radiation beam BM-BS2 andmay be adapted to transmit several horizontal radiation beams, which arenot shown in FIG. 1 for simplification.

The radio access network RAN even further contains a mobile station MSwhich is located at a cell border of a second radio cell C2 of thesecond base station BS2 and in a cell overlap area COA between a firstradio cell C1 of the first base station BS1 and the second radio cellC2.

The radio access network RAN may be connected to a core network of aradio communication system, which is also not shown for simplification.The radio access network RAN may be for example a radio access networkof a cellular mobile communication system such as GSM/GPRS (GSM=GlobalSystem for Mobile Communication, GPRS=General Packet Radio Service),UMTS (UMTS=Universal Mobile Telecommunication Systems), HSPA (HSPA=HighSpeed Packet Access), LTE (LTE=Long Term Evolution) or LTE-Advanced,which are all standardized by 3GPP. Alternatively, the radio accessnetwork RAN may be a WLAN (WLAN=Wireless Local Area Network) which maybe based on one of the IEEE 802.11 standards. In a further alternative,the radio access network RAN may be for example a WiMAX network(WiMAX=Worldwide Interoperability for Microwave Access) based on one ofthe IEEE 802.16 standards for enabling a delivery of last mile wirelessbroadband access as an alternative to cable and DSL (DSL=DigitalSubscriber Line). In even further alternatives, the radio access networkRAN1 may be based on one of the CDMA family of standards includingcdmaOne, CDMA2000, and CDMA2000 EV-DO which are standardized by 3GPP2(3GPP2=3rd Generation Partnership Project 2).

The term “base station” may be considered synonymous to and/or referredto as a base transceiver station, access point base station, accesspoint, macro base station, macrocell, micro base station, microcell,femtocell, picocell etc. and may describe equipment that provideswireless connectivity via one or more radio links to one or more mobilestations. The first base station BS1 and the second base station BS2 maybe for example an LTE Node B, an IEEE 802.11 access point, a WiMAX basestation etc.

The term “macro base station” may be considered synonymous to and/orreferred to a base station, which provides a radio cell having a size ina range of several hundred meters up to several kilometers. A macro basestation usually has a maximum output power of typically tens of watts.

The term “micro base station” may be considered synonymous to and/orreferred to a base station, which provides a radio cell having a size ina range of several tens of meters up to hundred meters. A micro basestation usually has a maximum output power of typically several watts.

The term “macro cell” may be considered synonymous to and/or referred toa radio cell, which provides the widest range of all radio cell sizes.Macro cells are usually found in rural areas or along highways and areusually operated with transmit powers in a range of several 10 Watt.

The term “micro cell” may be considered synonymous to and/or referred toa radio cell in a cellular network served by a low power cellular basestation, covering a limited area (smaller than an area of a macro cell)such as a mall, a hotel, or a transportation hub. A microcell isreferred to a group of radio cells, which contain pico cells and femtocells.

The term “pico cell” may be considered synonymous to and/or referred toa small cellular base station typically covering a small area, such asin-building (offices, shopping malls, train stations, stock exchanges,etc.), or more recently in-aircraft. In cellular networks, pico cellsare typically used to extend coverage to indoor areas where outdoorsignals do not reach well, or to add network capacity in areas with verydense phone usage, such as train stations.

The term “femto cell” may be considered synonymous to and/or referred toa small, low-power cellular base station, typically designed for use ina home or small business. A broader term which is more widespread in theindustry is small cell, with femto cell as a subset.

The term “mobile station” may be considered synonymous to, and mayhereafter be occasionally referred to, as a mobile unit, mobile user,access terminal, user equipment, subscriber, user, remote station or asmall cell, pico cell or femto cell when located in a moving vehiclesuch as a bus, a train or even a car. Each of the mobile stations UE1,UE2 may be for example a cellular telephone, a smart phone, a portablecomputer, a pocket computer, a hand-held computer, a personal digitalassistant, a moving base station, a smart watch, a head mounted displaysuch as a Google glass or a car-mounted mobile device such as a repeateror relay.

The term “radio cell” may be considered synonymous to and/or referred toas radio cell, cell, radio sector, sector etc.

The first base station BS1 contains an antenna array AA1. A surfacenormal SN with respect to a radiating surface RS of the antenna arrayAA1 is used for defining elevation angles of vertical radiation beamsBM1-BS1, BM2-BS1, BM3-BS1, BM4-BS1, BM5-BS1, which are transmitted bythe antenna array AA1 of the first base station BS1.

The first base station BS1 transmits a first vertical radiation beamBM1-BS1 by applying a first elevation angle ELA1. The first elevationangle ELA1 may be defined as an angle between the surface normal SN anda beam direction MBD1 of the first vertical radiation beam BM1-BS1. Thefirst base station BS1 further transmits a second vertical radiationbeam BM2-BS1 by applying a second elevation angle. The second elevationangle ELA2 may be zero because the surface normal SN and a beamdirection MBD2 of the second vertical radiation beam BM2-BS1 may have asame direction as shown exemplarily in FIG. 1. In a same way, the firstbase station BS1 applies further elevation angles (not shown forsimplification) for further three vertical radiation beams BM3-BS1,BM4-BS1, BM5-BS1. The first base station BS1 may alternatively transmitonly two vertical radiation beams, more than five vertical radiationbeams such as eight vertical radiation beams.

The first beam direction points to a first coverage area CA1 as a resultof the first elevation angle, the second beam direction points to asecond coverage as a results of the second elevation angle and so on(only a further coverage area CA4 for the fourth vertical radiation beamBM4-BS1 is shown in FIG. 1 for simplification). Thereby, the firstcoverage area CA1 and the at least second coverage area are located atdifferent radial positions within the first radio cell C1 of the firstbase station BS1. Radial position means for example a position with aspecific mean distance to a centre of the first radio cell C1 or with aspecific mean distance to a location of an antenna mast for the antennaarray AA1.

The second base station BS2 may have adjusted a beam direction MBD ofthe single vertical radiation beam BM-BS2 towards the mobile station MSfor serving the mobile station MS via the vertical radiation beamBM-BS2.

The vertical radiation beams BM1-BS1, BM2-BS1, BM3-BS1, BM4-BS1, BM5-BS1may be applied at a same time and independently from each other. Thismeans, that the first vertical radiation beam BM1-BS1 may be directed tothe mobile station MS, which is located in the cell overlap area betweenthe first radio cell C1 and the second radio cell C2 and for example thefourth vertical radiation beam BM4-BS1 may be directed to a furthermobile station, which may be located more closer to a centre of thefirst radio cell C1. In a further embodiment, a mobile station may beserved at a same time by one vertical radiation beam on a firstfrequency resource such as a first OFDM frequency subcarrier and by afurther vertical radiation beam on a second frequency resource such as asecond OFDM frequency subcarrier.

As already mentioned above a transmission of horizontal radiation beamsby the first base station BS1 and by the second base station BS2 towardsseveral radial directions around locations of antenna systems of thefirst base station BS1 and the second base station BS2 by usingdifferent azimuth angles is not shown in FIG. 1 for simplification. Anazimuth angle may be defined for example as an angle between the surfacenormal of the radiating surface of the antenna array AA1 and a beamdirection of a horizontal radiation beam.

Further base stations of the radio access network RAN and further mobilestations being connected to the radio access network RAN are not shownfor simplification. The features of the methods and the network nodesBS1, BS2 and MS which are described in the following with respect to thefirst base station BS1 being a neighbouring base station of the secondbase station BS2 may be extended to further neighbouring base stationsof the second base station BS2 which are not shown in FIG. 1 and are notdescribed in the following for simplification.

The radio access network RAN further contains a first backhaul link BHL1between the first base station BS1 and the second base station BS2 suchas an X2 interface which is defined by 3GPP. The X2 interface in LTE isused for a direct information exchange between the first base stationBS1 and the second base station BS2. Therefore, the first base stationBS1 and the second base station BS2 establish a so-called NRT(NRT=Neighbour Relation Table). This allows to directly requestparameters such as radio resource information for reference signals fromeach other.

Alternatively and optionally, the radio access network RAN may furthercontain a central database CDB for storing radio resource information ofreference signals, which are transmitted via vertical radiation beamswithin a predefined area of the radio access network RAN or by apredefined number of base stations of the radio access network RAN. Thesecond base station BS2 may be connected to the central database CDB bya second backhaul link BHL2. The central database CDB may be an O&Mdatabase (O&M=Operation and Maintenance), which usually contains systemrelevant parameters for operating a radio communication system.

The term “reference signal” may be considered synonymous to and/orreferred to as a CRS (CRS=common reference symbol), CSI reference symbol(CSI=Channel State Information), common pilot, common pilot signal,common pilot symbol, beacon, beacon signal etc. which is transmitted ina multicast or broadcast to all mobile stations in a radio cell or radiosector.

Basically an operation between the first base station BS1, the secondbase station BS2 and the mobile station MS is as follows:

Preferably, when the mobile station MS is located at the cell border ofthe second radio cell C2 in the cell overlap area COA, the second basestation BS2 for example transmits to the mobile station MS first radioresource information for a transmission of first reference signals viathe first radiation beam BM1-BS1 and at least second radio resourceinformation for a transmission of at least second reference signals viathe second radiation beam BM2-BS1. This means the first radio resourceinformation and the at least second radio resource information may betransmitted for a sub-group of the vertical radiation beams BM1-BS1, . .. , BM5-BS1. Alternatively, the radio resource information for atransmission of reference signals from each one of the verticalradiation beams BM1-BS1, . . . , BM5-BS1 may be transmitted from thesecond base station BS2 to the mobile station MS. A reception of thefirst radio resource information and the at least second radio resourceinformation at the mobile station MS allows the mobile station MS toreceive and detect the first reference signals and the at least secondreference signals.

The first radio resource information and the at least second radioresource information may be preferably transmitted to the mobile stationMS as a mapping list, which contains identifiers for the verticalradiation beams BM1-BS1, . . . , BM5-BS1 and identifiers for thereference signals such as indications for time resources, frequencyresources, sets of time resources and frequency resources and/or coderesources. The time resources may be for example sub-frames of 1 ms suchas applied in LTE. The frequency resources may be for example OFDMfrequency subcarriers such as applied in LTE. The code resources may befor example spreading codes such as applied in UMTS. The sets of timeresources and frequency resources may be for example sets of time andfrequency positions of resource elements, i.e. intersections of OFDMframes and subcarriers such as applied in LTE. The first radio resourceinformation and the at least second radio resource information may betransmitted from the first base station BS1 via the second base stationBS to the mobile station MS or directly via a broadcast from the firstbase station BS1 to the mobile station MS.

The reference signals need to be transmitted via the vertical radiationbeams BM1-BS1, . . . , BM5-BS1 in such a way, that a mobile station isable to distinguish the vertical radiation beams BM1-BS1, . . . ,BM5-BS1. If this differentiation is done for example in a time domain,in a first time period the reference signals are transmitted via a firstone of the vertical radiation beams BM1-BS1, . . . , BM5-BS1, in asecond time period the reference signals are transmitted via a secondone of the vertical radiation beams BM1-BS1, . . . , BM5-BS1 and so on.

For data transmissions from the first base station BS1 to mobilestations served by the first base station BS1 each one of the verticalradiation beams BM1-BS1, BM2-BS1, BM3-BS1, BM4-BS1, BM5-BS1 may becombined by each one of the horizontal radiation beams. While thereference signals are pre-coded in vertical direction to form apredefined number of vertical radiation beams, e.g. in time multiplex,in horizontal direction, each one of the antenna elements, which isarranged at a specific position in horizontal direction H-DIR (see FIG.7) of the antenna array AA1 (denoted as antenna system ANT-SYS-BS1 inFIG. 7), has its own set of orthogonal reference signals. In this way,the mobile station MS is adapted to determine a best vertical radiationbeam based on the signal quality for the pre-coded vertical referencesignals. Furthermore, the mobile station MS is adapted to calculate abest horizontal vertical radiation beam based on the orthogonalreference signals being received per horizontal antenna element.

This means, that the mobile station MS is able to differentiate antennaelements at the different positions in the horizontal direction H-DIR.Due to the pre-coding in the vertical direction, the mobile station MSis adapted to observe or perceive the antenna elements, which arearranged at different positions in vertical direction V-DIR (see FIG. 7)of the antenna array AA1, as a single antenna element. Thereby, themobile station MS is able to detect the different antenna elements beingarranged in the horizontal direction H-DIR but observes a see-saw likejumping of a signal quality based for example on the differentiation ofthe vertical radiation beams in the time domain as described above.

The same principle may be preferably applied also for the second basestation BS2.

The mobile station MS determines first quality information for the firstradiation beam BM1-BS1 based on the received first reference signals andat least second quality information for the at least second radiationbeam BM2-BS1, . . . , BM5-BS1 based on the received at least secondreference signals. Coverage areas of the first radiation beam BM1-BS1and the at least second radiation beam BM2-BS1, . . . , BM5-BS1 may bealso interpreted as candidate cells of the mobile station MS.

Then the mobile station MS transmits at least one of the first qualityinformation and the at least second quality information to the secondbase station BS2. A reception of the at least one of the first and theat least second quality information allows the second base station BS2to determine based on the at least one of the first quality informationand the at least second quality information whether a further schedulingof the mobile station MS by the second base station BS2 or a handover ofthe mobile station MS to one of the vertical radiation beams BM1-BS1, .. . , BM5-BS1 of the first base station BS1 is more suitable. In oneembodiment, the mobile station MS may transmit only quality informationfor a best vertical radiation beam BM1-BS1, . . . , BM5-BS1 to thesecond base station BS2.

When for example the second base station BS2 decides for the furtherscheduling of the mobile station MS, the second base station BS2 mayschedule the mobile station MS for uplink data and/or downlink databased on the at least one of the first quality information and the atleast second quality information in at least one time slot, when a usageof at least one of the first vertical radiation beam BM1-BS1 and of theat least one second vertical radiation beam BM2-BS1, . . . , BM5-BS1 bythe first base station BS1 fulfills a predefined criterion such as thatthe at least one of the first vertical radiation beam BM1-BS1 and of theat least one second vertical radiation beam BM2-BS1, . . . , BM5-BS1will not used by the first base station BS1 during the at least one timeslot.

When alternatively the second base station BS2 decides for a handover ofthe mobile station MS to the first base station BS1, the second basestation BS2 determines based on the at least one of the first qualityinformation and the at least second quality information one of the firstvertical radiation beam BM1-BS1 and of the at least one second verticalradiation beam BM2-BS1, . . . , BM5-BS1 as an initial serving radiationbeam to be applied at the first base station BS1 for serving the mobilestation MS after the handover from the second base station BS2 to thefirst base station BS1. In such a case, the second base station BS2transmits beam information of the selected initial serving radiationbeam to the first base station BS1. When receiving the beam information,the first base station BS1 applies the selected initial servingradiation beam for serving the mobile station MS for scheduling themobile station MS.

More details about the methods being applied by the mobile station MS,the second base station BS2 and the first base station BS1 are describedwith respect to following FIGS. 2, 3 and 4.

A technical description is given above with respect to FIG. 1 and belowwith respect to FIGS. 2 to 7 for a preferred embodiment of verticalradiation beams. In an alternative embodiment, the vertical radiationbeams may be replaced by horizontal radiation beams or by a mixture ofvertical radiation beams and horizontal radiation beams.

FIG. 2 shows schematically a flow diagram of a method MET-MS for themobile station MS for executing mobile station related process steps fora treatment or administration of the vertical radiation beams BM1-BS1, .. . , BM5-BS1 in the radio access network RAN.

In a first step S1-MS, the mobile station MS receives the first radioresource information for the first reference signals and the at leastsecond radio resource information for the second reference signals andpreferably for further reference signals being transmitted via thevertical radiation beams BM3-BS1, BM4-BS1, BM5-BS1. In a firstalternative, the mobile station MS may receive the first radio resourceinformation and the at least second radio resource information from thesecond base station BS2 for example by an RRC message (RRC=RadioResource Control) such as applied in 3GPP radio communication systems.In a second alternative, the mobile station MS may receive the firstradio resource information and the at least second radio resourceinformation directly from the first base station BS1 for example by abroadcast message on a broadcast channel.

In a first embodiment, when a same type of reference signals areperiodically switched between the first vertical radiation beam BM1-BS1and the at least one second vertical radiation beam BM2-BS1, . . . ,BM5-BS1, the first vertical radiation beam BM1-BS1 and the at least onesecond vertical radiation beam BM2-BS1, . . . , BM5-BS1 are periodicallypre-coded with one of a group of vertical pre-codings, which are appliedfor the first vertical radiation beam BM1-BS1 and for the at least onesecond vertical radiation beam BM2-BS1, . . . , BM5-BS1. In such a case,the first radio resource information comprises a first indication forfirst time resources or first timing information such as information ofa first periodic time slot for a preferably periodic transmission of thefirst reference signals. In a same way, the at least second radioresource information comprises at least one second indication for secondtime resources or second timing information such as information of asecond periodic time slot for a preferably periodic transmission of theat least second reference signals.

In a second embodiment, when a same type of reference signals areperiodically switched between the first vertical radiation beam BM1-BS1and the at least one second vertical radiation beam BM2-BS1, . . . ,BM5-BS1, the first radio resource information contains first indicationsfor example for positions of the first reference signals within a firstgrid of time resources and frequency resources. In a same way, the atleast second radio resource information contains at least secondindications for example for positions of the at least second referencesignals within at least one second grid of time resources and frequencyresources. In LTE for example, the reference signals are located in eachsub-frame and in each first and sixth OFDM symbol at subcarrierpositions 6, 12, 18, . . . and in each third and ninth OFDM symbol atsubcarrier positions 3, 9, 15, . . . . In a preferred embodiment,reference signals of a first sub-frame are used for the first verticalradiation beam BM1-BS1, reference signals of a second sub-frame are usedfor a second one of the at least one second vertical radiation beamBM2-BS1, . . . , BM5-BS1 and so on. In an alternative embodiment,frequency positions of the reference signals may be distributed acrossthe first vertical radiation beam BM1-BS1 and the at least one secondvertical radiation beam BM2-BS1, . . . , BM5-BS1.

In a third embodiment each one of the vertical radiation beams BM1-BS1,. . . , BM5-BS1 may have a different code resource such as a differentspreading code. Thereby, several or all of the vertical radiation beamsBM1-BS1, . . . , BM5-BS1 may be measured simultaneously by the mobilestation MS. In this case, the first radio resource information containsfor example a first indication for a first spreading code being appliedfor a transmission of the first reference signals. In a same way, the atleast second radio resource information contains for example at leastone second indication for at least one second spreading code beingapplied for a transmission of the at least second reference signals.

With respect to the first, second or thirds embodiments given above, thefirst radio resource information may contain a further indication forthe first radiation beam BM1-BS1 and the at least second radio resourceinformation may contain a further indication for the second radiationbeam BM2-BS1 or for the second radiation beam BM2-BS1 and for at leastone of the further radiation beams BM3-BS1, BM4-BS1, BM5-BS1.

The mobile station MS uses the first radio resource information and theat least second radio resource information to synchronize in time areceiver apparatus of the mobile station MS to the various timemultiplexed reference signals with respect to the first embodiment or tosynchronize in frequency the receiver apparatus of the mobile station MSto the various frequency multiplexed reference signals with respect tothe second embodiment or uses the first radio resource information andthe at least second radio resource information to adapt a decoding ofthe receiver apparatus to the various spreading codes of the referencesignals.

By a further step S2-MS, the mobile station MS receives the firstreference signals and with at least one further step S3-MS, the mobilestation MS receives the at least one second reference signal.

In step S4-MS the mobile station MS may determine the first qualityinformation for the first vertical radiation beam BM1-BS1 based on ananalysis of the received first reference signals and the at least secondquality information for one of the at least second vertical radiationbeam BM2-BS1, . . . , BM5-BS1 based on received corresponding referencesignals or may determine quality information for each of the verticalradiation beams BM1-BS1, . . . , BM5-BS1 for which reference signalscould be received with sufficient receive power. The first qualityinformation and the at least second quality information may be forexample received signal levels such as signal strength values, SINRvalues (SINR=Signal to Interference-plus-Noise Ratio) or a supportedModulation and Coding Scheme (MCS) of the received first and at leastsecond reference signals. A specific signal strength, SINR, or MCS valuefor a certain vertical radiation beam corresponds to a specificinterference level of the vertical radiation beams BM1-BS1, . . . ,BM5-BS1 at a location of the mobile station MS. The higher the signalstrength, SINR or the MCS value, the higher is the interference level.

By a further step S5-MS, the mobile station MS transmits at least one ofthe first quality information and the at least second qualityinformation and may be also quality information for the further verticalradiation beams BM3-BS1, . . . , BM5-BS1 to the second base station BS2.Therefore, the mobile station MS may use for example a handover requestmessage such as a so-called A3 message as applied by the 3GPP 36.331radio communication standard. The mobile station MS may transmit qualityinformation in various variants. Preferably, the mobile station MStransmits only quality information of one of the first verticalradiation beam BM1-BS1 and of the at least second vertical radiationbeam BM2-BS1, . . . , BM5-BS1 which provides a highest quality such as alargest received signal level. For giving the second base station BS2 alarger leeway in decision-making, the mobile station MS mayalternatively transmit quality information for a subgroup with at leasttwo of all received vertical radiation beams BM1-BS1, . . . , BM5-BS1 ormay transmit quality information for all of the received verticalradiation beams BM1-BS1, . . . , BM5-BS1.

In step S6-MS the mobile station MS verifies whether a handover commandmessage may have been received at the mobile station MS from the secondbase station BS2. When no such handover command message has beenreceived, the method MET-MS may be continued by the step S2-MS. Whenelse the handover command message has been received, the method MET-MSmay be continued by step S7-MS. The handover command message may containfor example information, that the mobile station MS may detach from thesecond radio cell C2 and may attach to an indicated one of the verticalradiation beams BM1-BS1, . . . , BM5-BS1 of the first radio cell C1.

With a further step S7-MS, the mobile station MS executes a handoverfrom the second radio cell C2 to the indicated one of the verticalradiation beams BM1-BS1, . . . , BM5-BS1 of the first radio cell C1.

A further step after the step S7-MS may be again the step S1-MS. For thefurther method now the roles of the first base station BS1 and thesecond base station BS2 are interchanged.

FIG. 3 shows schematically a flow diagram of a method MET-BS2 for thesecond base station BS2 for executing base station related process stepsof a serving base station for a treatment or administration of thevertical radiation beams BM1-BS1, . . . , BM5-BS1 in the radio accessnetwork RAN.

According to a first alternative, a knowledge of the first radioresource information and the at least second radio resource informationat the second base station BS2 may be pre-configured and stored in alocal database of the second base station BS2 for a transmission ofreference signals via vertical radiation beams of all neighboring basestations of the second base station BS2 when the second base station isinstalled. In such a case no request messages needs to be exchangedbetween the second base station BS2 and the neighboring base stationssuch as the first base station BS1 as long as a configuration fortransmitting the vertical radiation beams at one of the neighboring basestations is not changed. When no such pre-configuration may be appliedin a first step S1-BS2, the second base station BS2 may transmit amessage to the first base station BS1 for requesting the first radioresource information of the first reference signals and the at leastsecond radio resource information of the second reference signals andmay be also further reference signals of the further vertical radiationbeams BM3-BS1, . . . , BM5-BS1.

Alternatively, the second base station BS2 may transmit the message tothe central database CDB for requesting the first radio resourceinformation of the first reference signals and the at least second radioresource information of the at least second reference signals beingtransmitted via the vertical radiation beams BM1-BS1, . . . , BM5-BS1 ofthe first base station BS1.

When receiving the first radio resource information and the at leastsecond radio resource information from the first base station BS1 orfrom the central database CDB, the second base station BS2 may store bya further step S2-BS2 the first radio resource information and the atleast second radio resource information in the local database of thesecond base station BS2.

In a further step S3-BS2, when a mobile station such as the mobilestation MS arrives at a border of the second radio cell C2 and at thecell overlap area COA, the second base station BS2 may query the firstradio resource information of the first reference signals and the atleast second radio resource information of the at least second referencesignals being transmitted via the vertical radiation beams BM1-BS1, . .. , BM5-BS1 from its own local database and transmits the first radioresource information and the at least second radio resource informationto the mobile station MS.

In a next step S4-BS2, the second base station BS2 receives the at leastone of the first quality information and/or the at least second qualityinformation and may be also quality information for the further verticalradiation beams BM3-BS1, . . . , BM5-BS1 from the mobile station MS. Thestep S4-BS2 may be a first step, when the first radio resourceinformation and the at least second radio resource information aredirectly transmitted from the first base station BS1 via the broadcastmessage to the mobile station MS. The dashed arrow shows an alternativeembodiment, when the method MET-BS2 may not contain the steps S1-BS2,S2-BS2 and S3-BS2.

By a further step S5-BS2, the second base station BS2 determines basedon the at least one of the first quality information and the at leastsecond quality information, whether a further scheduling of the mobilestation MS by the second base station BS2 or a handover or cellre-association of the mobile station MS to one of the vertical radiationbeams BM1-BS1, . . . , BM5-BS1 of the first base station BS1 is moresuitable. The second base station BS2 decides for the handover or thecell re-association, when for example one of the vertical radiationbeams BM1-BS1 . . . BM2-BS1 has a higher receive signal level, a higherSINR, or a higher supported MCS at the mobile station MS compared to thecurrently applied vertical radiation beam BM-BS2 of the second basestation BS2 for scheduling the mobile station MS.

In such a case, step S9-BS2 is a next step. Else the method MET-BS2 iscontinued by a further step S6-BS2.

By the step S6-BS2, the second base station BS2 may transmit a requestto the first base station BS1 for getting information regarding a usageof the first radiation beam BM1-BS1 and of the at least one secondradiation beam BM2-BS1, . . . , BM5-BS1 by the first base station BS1for transmitting downlink data to mobile stations being served by thefirst base station BS1 and preferably further regarding a transmissionof uplink data by the mobile stations to the first base station BS1.

In a further step S7-BS2, the second base station BS2 may receive theinformation regarding the usage of the first radiation beam BM1-BS1 andof the at least one second radiation beam BM2-BS1, . . . , BM5-BS1 andpreferably regarding a transmission of uplink data by the mobilestations to the first base station BS1 from the first base station BS1.The information may indicate for example one or several of the verticalradiation beams BM1-BS1, . . . , BM5-BS1 and may further indicate one orseveral time slots or a time frame containing several time slots for apredefined time in the future such as e.g. 10 ms or 20 ms when the firstbase station BS1 will not use the one or several of the verticalradiation beams BM1-BS1, . . . , BM5-BS1 for scheduling mobile stationswhich are served by the first base station BS1. The information maypreferably further indicate for the one or several time slots, for thetime frame containing the several time slots of for one or severalfurther time slots in each case within a predefined time in the futuresuch as e.g. 10 ms or 20 ms when the mobile stations served by the firstbase station BS1 will transmit uplink data to the first base stationBS1.

The information may be repeatedly sent from the first base station BS1for a predefined time after receiving the request from the second basestation BS2.

In a next step S8-BS2, the second base station BS2 may schedule themobile station MS in one of the time slots or time frames as indicatedby the first base station BS1 because during such time slots or timeframes a radio transmission between the second base station BS2 and themobile station MS is less impacted by interference which is generated bydata transmission and by transmission of dedicated pilot (so-calleddemodulation reference symbols DRS) via the vertical radiation beamsBM1-BS1, . . . , BM5-BS1 of the first base station BS1. A further stepafter the step S8-BS2 may be the step S4-BS2.

Alternatively, the second base station BS2 may prevent a scheduling ofthe mobile station MS for uplink data in the at least one time slot orthe at least one further time slot, when during the at least one timeslot or the at least one further time slot uplink data are transmittedto the first base station BS1 from at least one of the mobile stationsbe served by the first base station BS1.

In step S9-BS2, the second base station BS2 may transmit a handoverrequest message to the first base station BS1 for requesting a handoverfrom the second base station BS2 to the first base station BS1 as aso-called target base station for the mobile station MS. A next stepafter the step S9-BS2 may be step S10-BS2 or step S12-BS2.

By the step S10-BS2, the second base station BS2 may receive from thefirst base station BS1 a handover reject message that the handover isrejected by the first base station BS1. In such a case, the second basestation BS2 may continue by a further step S11-BS2 scheduling the mobilestation MS in one of the time slots or time frames as indicated by thefirst base station BS1.

By the step S12-BS2, the second base station BS2 may else receive fromthe first base station BS1 a handover accept message that the handoveris accepted by the first base station BS1. In such a case, the secondbase station BS2 determines in a further step S13-BS2 based on thequality information received from the mobile station MS one of thevertical radiation beams BM1-BS1, . . . , BM5-BS1 as an initial servingradiation beam for serving the mobile station MS at the first basestation BS1 after the handover from the second base station BS2 to thefirst base station BS1.

In a next step S14-BS2, the second base station BS2 transmits beaminformation of the selected initial serving radiation beam to the firstbase station BS1. The beam information contains at least one identifierfor the selected initial serving radiation beam and may preferably alsocontain quality information of the selected initial serving radiationbeam. The quality information may be for example quality information asbeing received at the second base station BS2 from the mobile station MSbefore the handover is executed. This means, that the qualityinformation may be for example a CQI value or a receive signal levelpreferably as lastly measured and reported by the mobile station MS tothe second base station BS2 before the handover of the mobile station MSfrom the second base station BS2 to the first base station BS1 isexecuted.

FIG. 4 shows schematically a flow diagram of a method MET-BS1 for thefirst base station BS1 for executing base station related process stepsof a neighboring base station for a treatment or administration ofvertical radiation beams BM1-BS1, . . . , BM5-BS1 in the radio accessnetwork RAN.

In a first step S1-BS1, the first base station BS1 transmits the firstreference signals via the first vertical radiation beam BM1-BS1, thesecond reference signals via the second vertical radiation beam BM2-BS1,and corresponding reference signals via the further vertical radiationbeams BM3-BS1, . . . , BM5-BS1.

By a further optional step S2-BS1, the first base station BS1 mayreceive the message from the second base station BS2 for requesting thefirst radio resource information and the at least second radio resourceinformation.

In a next optional step S3-BS1, the first base station BS1 transmits thefirst radio resource information and the at least second radio resourceinformation to the second base station BS2.

According to an alternative embodiment with respect to the steps S2-BS1and S3-BS1, the first base station BS1 may transmit by the broadcastmessage via the broadcast channel the first radio resource informationand the at least second radio resource information.

In a further step S4-BS1, the first base station BS1 receives therequest from the second base station BS2 for providing informationregarding the usage of the first radiation beam BM1-BS1 and of the atleast one second radiation beam BM2-BS1, . . . , BM5-BS1 by the firstbase station BS1.

In a next step S5-BS1, the first base station BS1 transmits theinformation regarding the usage of the first radiation beam BM1-BS1 andof the at least one second radiation beam BM2-BS1, . . . , BM5-BS1 tothe second base station BS2.

In a further step S6-BS1, the first base station BS1 receives thehandover request message from the second base station BS2.

By a next step S7-BS1, the first base station BS1 verifies, whether thehandover of the mobile station MS from the second base station BS2 tothe first base station BS1 shall be accepted or rejected. A decisionmaking at the first base station BS1 may depend for example on a currentload situation at the first base station BS1. When the handover isrejected by the first base station BS1, step S8 a-BS1 may be a nextstep. Else when the handover is rejected by the first base station BS1,step S8 b-BS1 may be a further step.

By the step S8 a-BS1, the first base station BS1 transmits the handoverreject message to the second base station BS2. A next step after thestep S8 a-BS1 may be again the step S6-BS1.

Using the step S8 b-BS1, the first base station BS1 transmits thehandover accept message to the second base station BS2.

In a further step S9-BS1, the first base station BS1 receives from thesecond base station BS2 the beam information of the initial servingradiation beam as selected by the second base station BS2. In current3GPP standards a target base station has no information and gets noinformation about a channel quality and a PMI (PMI=Precoding MatrixIndication) directly after a handover and before a first CQI measurementis received from a mobile station which has executed the handover. Thebeam information allows the first base station BS1 to automaticallyselect a suitable vertical radiation beam at a beginning of a timeperiod for serving the mobile station MS.

In a next step S10-BS1, the first base station BS1 schedules the mobilestation MS directly after the handover by the initial serving radiationbeam as selected by the second base station BS2.

By further step S11-BS1, the first base station BS1 may receive from themobile station MS further quality information of at least one of thevertical radiation beams BM1-BS1, . . . , BM5-BS1 and the verticalradiation beam BM-BS2 in a similar way as the step S4-BS2 which isexecuted by the second base station BS2.

In step S12-BS1, the first base station BS1 verifies based on thereceived further quality information whether a better alternative as theinitial serving radiation beam for serving the mobile station MS exists.For such verification the first base station BS1 may compare for examplereceived signals levels. When no better alternative exists, a next stepafter the step S12-BS1 may be again the step S10-BS1. When else anothervertical radiation beam with for example a larger received signal levelthan the initial serving radiation beam exists, a next step after thestep S12-BS1 may be step S13-BS1.

By the step S12-BS1, the first base station BS1 may perform a beamswitching for the mobile station MS and may schedule the mobile stationMS by the further vertical radiation beam.

FIG. 5 shows schematically an exemplarily block diagram of the mobilestation MS. The mobile station MS contains an antenna system ANT-SYS-MSand a transceiver MS-TRC for transmitting uplink radio frequency signalstowards the first base station BS1 or the second base station BS2 andfor receiving downlink radio frequency signals from the first basestation BS1 or the second base station BS2 via the antenna systemANT-SYS-MS. The antenna system ANT-SYS-MS exemplarily contains twoantenna elements but may alternatively contain only a single antennaelement or more than two antenna elements.

The transceiver TRC-MS contains a transmitter part TR-MS and a receiverpart RC-MS. Alternatively, the mobile station MS may contain instead ofthe transceiver TRC-MS a separate transmitter and a separate receiver.

The transceiver TRC-MS and the antenna system ANT-SYS-MS are adapted forreceiving from the second base station BS2 the first radio resourceinformation and the at least second radio resource information, forreceiving the first reference signals based on the first radio resourceinformation and for receiving the at least second reference signalsbased on the at least second radio resource information. The transceiverTRC-MS and the antenna system ANT-SYS-MS are further adapted fortransmitting the at least one of the first quality information and ofthe at least second quality information to the second base station BS2.

The mobile station MS further contains a memory MEM-MS for storing acomputer program PROG-MS which contains commands for executing themethod MET-MS. The mobile station MS further contain a processing unitPU-MS for executing the computer program PROG-MS. The processing unitPU-MS and the computer program PROG-MS are for example adapted todetermine the first quality information for the first radiation beamBM1-BS1 based on the received first reference signals and the at leastsecond quality information for the at least one second radiation beamBM2-BS1, . . . , BM5-BS1 based on the received at least second referencesignals.

FIG. 6 shows schematically an exemplarily block diagram of the secondbase station BS2. The second base station BS2 contains an antenna systemANT-SYS-BS2 and a first transceiver TRC1-BS2 for transmitting downlinkradio frequency signals towards the mobile station MS and for receivinguplink radio frequency signals from the mobile station MS via theantenna system ANT-SYS-BS2. The first transceiver TRC1-BS2 contains atransmitter part TR1-BS2 and a receiver part RC1-BS2. Alternatively, thesecond base station BS2 may contain instead of the transceiver TRC1-BS2a separate transmitter and a separate receiver.

The antenna system ANT-SYS-BS2 may be for example a linear antenna arraywhich contains exemplarily 4 antenna elements in a 1 (vertical)×4(horizontal) arrangement. The linear antenna array in horizontaldirection H-DIR with respect to the Earth's surface allows transmittingseveral horizontal radiation beams towards different radial directionsfrom a centre of the second radio cell C2 towards the border of thesecond radio cell C2. Alternatively, the antenna system ANT-SYS-BS1 maycontain less than 4 antenna elements such as 2 antenna elements in a 1×2arrangement or more than 4 antenna elements such as 8 antenna elementsin a 1×8 arrangement.

The first transceiver TRC1-BS2 and the antenna system ANT-SYS-BS2 areadapted for transmitting to the mobile station MS the first radioresource information for the transmission of the first reference signalsvia the first radiation beam BM1-BS1 being directed by the first basestation BS1 towards the first direction and the at least second radioresource information for the transmission of the at least secondreference signals via the at least one second radiation beam BM2-BS1, .. . , BM5-BS1 directed by the first base station BS1 towards the atleast one second direction. The first transceiver TRC1-BS2 and theantenna system ANT-SYS-BS2 are further adapted for receiving from themobile station MS2 the at least one of first quality information of thefirst radiation beam BM1-BS1 and the at least second quality informationof the at least one second radiation beam BM2-BS1, . . . , BM5-BS1.

The second base station BS2 further contains a first cable connectionCC1 and a second transceiver TRC2-BS2 which is connected to the firstcable connection CC1. The second transceiver TRC2-BS2 contains atransmitter part TR2-BS2 and a receiver part RC2-BS2. Alternatively, thesecond base station BS2 may contain instead of the second transceiverTRC2-BS2 a further separate transmitter and a further separate receiver.The second transceiver TRC2-BS2 may be adapted to communicate with acorresponding transceiver of the first base station BS1.

According an alternative embodiment, the first backhaul connection BHL1may be realized by a wireless connection between the first base stationBS1 and the second base station BS2.

The second base station BS2 may even further contain a second cableconnection CC2 and a third transceiver TRC3-BS2 which is connected tothe second cable connection CC2. The third transceiver TRC3-BS2 containsa transmitter part TR3-BS2 and a receiver part RC3-BS2. Alternatively,the second base station BS2 may contain instead of the third transceiverTRC3-BS2 an even further separate transmitter and an even furtherseparate receiver. The third transceiver TRC3-BS1 may be adapted tocommunicate with the central database CDB.

The second base station BS2 even further contains a memory MEM-BS2 forstoring a computer program PROG-BS2 which contains commands forexecuting the method MET-BS2. The memory MEM-BS2 may be further adaptedfor storing a local database LDB-BS2. The local database LDB-BS2 maystore the first radio resource information and the at least second radioresource information. The local database LDB-BS2 may further storeinformation of time slots or time frames of the vertical radiation beamsof the base stations in the neighborhood of the second base station BS2,when these vertical radiation beams are not used for scheduling mobilestations.

The second base station BS2 further contains a processing unit PU-BS2for executing the computer program PROG-BS2. The processing unit PU-BS2and the computer program PROG-BS2 are adapted for example to determinebased on the at least one of the first quality information and the atleast second quality information whether a further scheduling of themobile station MS by the second base station BS2 or a handover for themobile station MS towards the first base station BS1 is more suitable.

FIG. 7 shows schematically an exemplarily block diagram of the firstbase station BS1. The first base station BS1 contains an antenna systemANT-SYS-BS1 and a first transceiver TRC1-BS1 for transmitting downlinkradio frequency signals towards the mobile station MS and for receivinguplink radio frequency signals from the mobile station MS via theantenna system ANT-SYS-BS1. The first transceiver TRC1-BS1 contains atransmitter part TR1-BS1 and a receiver part RC1-BS1. Alternatively, thefirst base station BS1 may contain instead of the first transceiverTRC1-BS1 a separate transmitter and a separate receiver.

The antenna system ANT-SYS-BS1 may be for example a rectangular planarantenna array which contains exemplarily 16 antenna elements in a 4(vertical)×4 (horizontal) arrangement. A first antenna stack in thevertical direction V-DIR with respect to the Earth's surface allowstransmitting the vertical radiation beams BM1-BS1, . . . , BM5-BS1 withdifferent elevation angles ELA1, ELA2 (not all elevation angles shown inFIG. 1 for simplification). A second antenna stack in the horizontaldirection H-DIR with respect to the Earth's surface allows transmittingseveral horizontal radiation beams towards different radial directionsfrom a centre of the first radio cell C1 towards a border of the firstradio cell C1. Alternatively, the antenna system ANT-SYS-BS1 may containless than 16 antenna elements such as 8 antenna elements in a 2×4arrangement or more than 16 antenna elements such as 32 antenna elementsin a 4×8 arrangement.

The first transceiver TRC1-BS1 and the antenna system ANT-SYS-BS1 areadapted for transmitting the first reference signals via the firstradiation beam BM1-BS1 directed towards the first direction and the atleast second reference signals via the at least one second radiationbeam BM2-BS1, . . . , BM5-BS1 directed towards the at least one seconddirection. The first transceiver TRC1-BS1 and the antenna systemANT-SYS-BS1 are further adapted for receiving for the handover of themobile station MS from the second base station BS2 to the first basestation BS1 quality information of one of the first radiation beamBM1-BS1 and of the at least one second radiation beam BM2-BS1, . . . ,BM5-BS1. The received quality information may be regarded as anindication that the corresponding vertical radiation beam shall beapplied by the first base station BS1 as an initial serving radiationbeam for serving the mobile station MS.

The first base station BS1 further contains for example a cableconnection CC and a second transceiver TRC2-BS1 which is connected tothe cable connection CC. The second transceiver TRC2-BS1 contains atransmitter part TR2-BS1 and a receiver part RC2-BS1. Alternatively, thefirst base station BS1 may contain instead of the second transceiverTRC2-BS1 a further separate transmitter and a further separate receiver.The second transceiver TRC2-BS1 may be adapted to communicate with thesecond transceiver TRC2-BS2 of the second base station BS2.

According an alternative embodiment, the first backhaul connection BHL1may be realized by a wireless connection between the first base stationBS1 and the second base station BS2.

The first base station BS1 even further contains a memory MEM-BS1 forstoring a computer program PROG-BS1 which contains commands forexecuting the method MET-BS1. The memory MEM-BS1 may be further adaptedfor storing a local database LDB-BS1. The local database LDB-BS1 maystore the first radio resource information and the at least second radioresource information. The local database LDB-BS1 may further storeinformation of time slots or time frames of the vertical radiation beamsof the base stations in the neighborhood of the first base station BS1,when these vertical radiation beams are not used for scheduling mobilestations such as the mobile station MS.

The first base station BS1 further contains a processing unit PU-BS1 forexecuting the computer program PROG-BS1. The processing unit PU-BS1, thecomputer program PROG-BS1 and the first transceiver TRC1-BS1 are forexample adapted to verify, whether a handover request from the secondbase station BS2 may be accepted or rejected, to interpret a receptionof the quality information of the initial serving radiation beam as arecommendation or a command from the second base station BS2 to schedulethe mobile station MS by the initial serving radiation beam and toverify, whether an alternative vertical radiation beam may be appliedfor the mobile station MS after receiving further quality information ofthe vertical radiation beams directly from the mobile station MS.

The description and drawings merely illustrate the principles of theinvention. It will thus be appreciated that those skilled in the artwill be able to devise various arrangements that, although notexplicitly described or shown herein, embody the principles of theinvention and are included within its spirit and scope. Furthermore, allexamples recited herein are principally intended expressly to be onlyfor pedagogical purposes to aid the reader in understanding theprinciples of the invention and the concepts contributed by theinventor(s) to furthering the art, and are to be construed as beingwithout limitation to such specifically recited examples and conditions.Moreover, all statements herein reciting principles, aspects, andembodiments of the invention, as well as specific examples thereof, areintended to encompass equivalents thereof.

Functional blocks denoted as “means for performing a certain function”shall be understood as functional blocks comprising circuitry that isadapted for performing the certain function, respectively. Hence, a“means for something” may as well be understood as a “means beingadapted or suited for something”. A means being adapted for performing acertain function does, hence, not imply that such means necessarily isperforming said function (at a given time instant).

Functions of various elements shown in the figures, including anyfunctional blocks may be provided through the use of dedicated hardware,as e.g. a processor, as well as hardware capable of executing softwarein association with appropriate software. When provided by a processor,the functions may be provided by a single dedicated processor, by asingle shared processor, or by a plurality of individual processors,some of which may be shared. Moreover, explicit use of the term“processor” or “controller” should not be construed to refer exclusivelyto hardware capable of executing software, and may implicitly include,without limitation, DSP hardware, network processor, ASIC, FPGA, readonly memory (ROM) for storing software, random access memory (RAM), andnon-volatile storage. Other hardware, conventional and/or custom, mayalso be included.

It should be appreciated by those skilled in the art that any blockdiagrams herein represent conceptual views of illustrative circuitryembodying the principles of the invention. Similarly, it will beappreciated that any flow charts, flow diagrams, state transitiondiagrams, pseudo code, and the like represent various processes whichmay be substantially represented in computer readable medium and soexecuted by a computer or processor, whether or not such computer orprocessor is explicitly shown.

Furthermore, the following claims are hereby incorporated into thedetailed description, where each claim may stand on its own as aseparate embodiment. While each claim may stand on its own as a separateembodiment, it is to be noted that—although a dependent claim may referin the claims to a specific combination with one or more otherclaims—other embodiments may also include a combination of the dependentclaim with the subject matter of each other dependent claim. Suchcombinations are proposed herein unless it is stated that a specificcombination is not intended. Furthermore, it is intended to include alsofeatures of a claim to any other independent claim even if this claim isnot directly made dependent to the independent claim.

It is further to be noted that the methods MET-MS, MET-BS1, MET-BS2disclosed in the specification or in the claims may be implemented by adevice having means for performing each of the respective steps of thesemethods. Preferably, a computer program product may containcomputer-executable instructions for performing the methods MET-MS,MET-BS1, MET-BS2, when the computer program product is executed on aprogrammable hardware device such as a DSP, an ASIC or an FPGA.Preferably, a digital data storage device may encode amachine-executable program of instructions to perform one of the methodsMET-MS, MET-BS1, MET-BS2.

Further, it is to be understood that the disclosure of multiple steps orfunctions disclosed in the specification or claims may not be construedas to be within the specific order. Therefore, the disclosure ofmultiple steps or functions will not limit these to a particular orderunless such steps or functions are not interchangeable for technicalreasons. Furthermore, in some embodiments a single step may include ormay be broken into multiple sub steps. Such sub steps may be includedand part of the disclosure of this single step unless explicitlyexcluded.

The invention claimed is:
 1. A method for operating a mobile station ina radio communication system comprising: receiving from a serving basestation of said mobile station first radio resource information for atransmission of first reference signals by an antenna array via a firstradiation beam being directed by at least one neighboring base stationof said serving base station towards a first direction and being alignedwith respect to a first elevation angle and at least one second radioresource information for a transmission of at least second referencesignals by said antenna array via at least one second radiation beamdirected by said at least one neighboring base station to at least onesecond direction and being aligned with respect to a second elevationangle different to said first elevation angle; receiving said firstreference signals based on said first radio resource information;receiving said at least second reference signals based on said at leastone second radio resource information; determining first qualityinformation of said first radiation beam (BM1-BS1) based on saidreceived first reference signals and at least second quality informationof said at least second radiation beam based on said received at leastsecond reference signals; and transmitting at least one of said firstquality information and said at least second quality information to saidserving base station.
 2. The method according to claim 1, wherein saidat least one of said first quality information and said at least secondquality information comprises either of the following: qualityinformation of one of said first radiation beam and of said at leastsecond radiation beam providing a highest quality; quality informationof at least two of said first radiation beam and of said at least secondradiation beam; quality information of all of said first radiation beamand of said at least second radiation beam.
 3. The method according toclaim 1, wherein said receiving of said first reference signals and saidreceiving of said at least second reference signals comprises receivingsaid first reference signals and said at least second reference signalsby either of the following: at least two time resources; at least twofrequency resources; at least two code resources; at least two differentsets of time resources and frequency resources.
 4. A method foroperating a base station in a radio communication system comprising:transmitting to a mobile station being served by said base station firstradio resource information for a transmission of first reference signalsby an antenna array via a first radiation beam being directed by atleast one neighboring base station of said base station towards a firstdirection and being aligned with respect to a first elevation angle andat least one second radio resource information for a transmission of atleast second reference signals by said antenna array via at least onesecond radiation beam directed by said at least one neighboring basestation to at least one second direction and being aligned with respectto a second elevation angle different to said first elevation angle;receiving from said mobile station at least one of a first qualityinformation of said first radiation beam, said first quality informationhaving been determined based on said first reference signals and of atleast second quality information of said at least one second radiationbeam, said second quality information having been determined based onsaid second reference signals; and determining based on said at leastone of said first quality information and said at least second qualityinformation, whether a further scheduling of said mobile station by saidbase station or a handover of said mobile station to said at least oneneighboring base station is more suitable.
 5. The method according toclaim 4, wherein said first radio resource information comprises atleast one first indication for at least one first time resource, atleast one first frequency resource or a first set of at least one firsttime resource and at least one first frequency resource for transmittingsaid first reference signals and wherein said at least one second radioresource information comprises at least one second indication for atleast one second time resource, at least one second frequency resourceor at least one second set of at least one second time resource and atleast one second frequency resource for transmitting said at leastsecond reference signals.
 6. The method according to claim 4, whereinsaid method further comprises scheduling said mobile station for uplinkdata and/or downlink data based on said at least one of said firstquality information and said at least second quality information in atleast one time slot, when a usage of said first radiation beam or ofsaid at least one second radiation beam by said at least one neighboringbase station fulfills a predefined criterion and when said mobilestation is in a coverage of said first radiation beam or of said atleast one second radiation beam.
 7. The method according to claim 6,said method further comprises: transmitting a handover request messageto said at least one neighboring base station for requesting a handoverof said mobile station to said at least one neighboring base station;receiving a handover reject message for said requested handover; andcontinuing scheduling said mobile station for said uplink data and/orsaid downlink data based on said at least one of said first qualityinformation and said at least second quality information in said atleast one time slot, when said usage of said first radiation beam or ofsaid at least one second radiation beam by said at least one neighboringbase station fulfills said predefined criterion and when a furtherhandover decision for said mobile station is pending.
 8. The methodaccording to claim 6, wherein said predefined criterion is anavailability of information at said base station that one of said firstradiation beam and of said at least one second radiation beam with alargest interference at a location of said mobile station is currentlynot used.
 9. The method according to claim 4, wherein said first radioresource information comprises at least one first indication for atleast one first code resource being applied for a transmission of saidfirst reference signals and wherein said at least one second radioresource information comprises at least one second indication for atleast one second code resource being applied for a transmission of saidat least second reference signals.
 10. The method according to claim 9,wherein said first radio resource information further indicates saidfirst radiation beam and wherein said at least one second radio resourceinformation further indicates said at least one second radiation beam.11. The method according to claim 4, wherein said method furthercomprises at least one of the following: requesting said first radioresource information and said at least one second radio resourceinformation from said at least one neighboring base station or from acentral database; storing said first radio resource information and saidat least one second radio resource information at a local database ofsaid base station.
 12. The method according to claim 4, wherein saidmethod further comprises: transmitting from said base station to atleast one neighboring base station a request for information about ausage of said first radiation beam and of said at least one secondradiation beam by said at least one at least one neighboring basestation; and receiving at said base station from said at least oneneighboring base station a reply with said information.
 13. The methodaccording to claim 12, wherein said usage information comprisesinformation about a scheduling of further mobile stations at said atleast one neighboring base station via said first radiation beam and/orvia said at least one second radiation beam.
 14. A mobile station foroperation in a radio communication system comprising: means forreceiving from a serving base station of said mobile station first radioresource information for a transmission of first reference signals by anantenna array via a first radiation beam being directed towards a firstdirection and being aligned with respect to a first elevation angle byat least one neighboring base station of said serving base station andat least second radio resource information for a transmission of atleast second reference signals by said antenna array via at least onesecond radiation beam being directed towards at least one seconddirection and being aligned with respect to a second elevation angledifferent to said first elevation angle by said at least one neighboringbase station, for receiving said first reference signals based on saidfirst radio resource information and for receiving said at least secondreference signals based on said at least second radio resourceinformation; means for determining first quality information of saidfirst radiation beam based on said received first reference signals andat least second quality information of said at least second radiationbeam based on said received at least second reference signals; and meansfor transmitting at least one of said first quality information and ofsaid at least second quality information to said serving base station.15. A base station for operation in a radio communication systemcomprising: means for transmitting to a mobile station being served bysaid base station first radio resource information for a transmission offirst reference signals by an antenna array via a first radiation beambeing directed by at least one neighboring base station of said basestation towards a first direction and being aligned with respect to afirst elevation angle and at least second radio resource information fora transmission of at least second reference signals by said antennaarray via at least one second radiation beam directed by said at leastone neighboring base station to at least one second direction and beingaligned with respect to a second elevation angle different to said firstelevation angle; means for receiving from said mobile station at leastone of a first quality information of said first radiation beam, saidfirst quality information having been determined based on said firstreference signals and of at least second quality information of said atleast one second radiation beam, said second quality information havingbeen determined based on said second reference signals; and means fordetermining based on said at least one of said first quality informationand said at least second quality information, whether a furtherscheduling of said mobile station by said base station or a handover ofsaid mobile station to said at least one neighboring base station ismore suitable.